1. Field of Invention
The present invention relates to magnetic sensors, such as an AT sensor, for use in a transmission of an automobile.
2. Related Art
Hitherto, as a sensor of such a kind, there has existed a sensor illustrated in FIGS. 14 and 15. This sensor is an AT sensor for use in an automobile, and has a coil AA and a drive oscillator circuit BB. In the coil AA, a metallic shaft CC is inserted. The drive oscillator circuit BB generates a high-frequency magnetic field in the coil AA. The coil AA of this sensor outputs detection signals according to an inserted state of the shaft CC, as indicated by a solid line in FIG. 16. Thus, the inserted state of the shaft CC can be detected. That is, it can be detected which of positions P to 3 shown in FIG. 14 the shaft CC moves and is inserted to.
In the conventional sensor, the characteristics of the coil AA itself vary with temperature. Therefore, the level of the detection signal outputted according to the inserted state of the shaft CC varies as indicated by dashed lines in FIG. 16. Consequently, the conventional sensor has a problem in that the position of the shaft cannot be accurately detected.
The present invention is accomplished by directing attention to this problem. Accordingly, an object of the present invention is to provide a magnetic sensor that can accurately detect the position of the shaft even when the characteristics of a coil itself vary according to a change in temperature or the like.
Another object of the present invention is to provide a magnetic sensor that is free from a magnetic influence to a sensor coil portion of a metal rotating shaft as an object to be detected, and the magnetic sensor is achieved to be minimized. Further, if the rotating shaft is thermally expanded, there is not changed the position relationship between the metal rotating shaft and the sensor coil portion, and the magnetic sensor is also free from the temperature compensation under the sensor mounting condition.
To resolve the problem, according to the first aspect of the present invention, there is provided a sensor that comprises a detection coil into which a metallic shaft to be detected, a reference coil having the same specifications as those for the detection coil, drive oscillator circuits for generating high-frequency magnetic fields in the detection coil and the reference coil, and a comparator for outputting a detection signal, which indicates that the shaft to be detected is detected, according to the difference between an oscillation signal, which is outputted from the detection coil according to an inserted state of the shaft to be detected, and an oscillation signal outputted from the reference coil.
A second aspect of the present invention is configured so that a reference shaft having the same specifications as those for the shaft to be detected is inserted into the reference coil, in the sensor according to the first aspect.
A third aspect of the present invention is configured so that the drive oscillator circuits are adapted to generate the high-frequency magnetic field according to the oscillation signal outputted from the reference coil, in the sensor according to the first or second aspect of the present invention.
A fourth aspect of the present invention is configured in such a manner as to further comprise shield members for providing magnetic shielding between the detection coil and the reference coil, in addition to the constituent elements of the sensor according to one of the first to third aspect.
A fifth aspect of the present invention, there is provided a sensor that comprises a detection coil, a reference coil, which is series-connected to the detection coil and has the same specifications as those for the detection coil, a metallic common shaft to be inserted into the detection coil and the reference coil so that a total of a dimension of a part thereof, which is inserted into the detection coil, and a dimension of a part thereof, which is inserted into the reference coil, is a predetermined dimension, a shaft to be detected, which is disposed in such a way as to be able to drive the common shaft in a direction in which the common shaft is inserted into each of the detection coil and the reference coil, drive oscillator circuits for generating high-frequency magnetic fields in the detection coil and the reference coil, and a comparator for outputting a detection signal, which indicates that the common shaft is detected, according to the difference between oscillation signals respectively outputted from the detection coil and the reference coil according to an inserted state of the common shaft.
A sixth aspect of the present invention is configured so that the drive oscillator circuits are adapted to generate the high-frequency magnetic field according to the oscillation signal outputted from the reference coil, in the sensor according to fifth aspect of the present invention.
A seventh aspect of the present invention is configured so that the detection coil and the reference coil constitute a bridge circuit together with a first bridge element and a second bridge element, and that each of the first and second bridge elements is a capacitor constituted by a chip component, in the sensor according to the fifth or sixth aspect.
According to the eighth aspect of the present invention, there is provided the magnetic sensor comprising a rotating shaft rotating interlockingly with the object to be detected, an arc-shaped metal member interlocked with the rotation of the rotating shaft and moving on a circular trajectory thereof with said rotating shaft serving as a center thereof, a sensor coil portion fixed on the circular trajectory with a center axis bending to an arc-shaped in order to freely adjust an occupation amount with respect to the magnetic circuit in response to the movement of the metal member into a center air core of the sensor coil portion and a sensor circuit generating a signal corresponding to a rotation angle of the rotation shaft by detecting a magnetically change of the sensor coil portion generated in response to the movement of the metal member in the sensor coil portion under a condition that a modulated magnetic field with a high frequency is generated by driving and exciting the sensor coil portion.
A ninth aspect of the present invention, there is provided a magnetic sensor comprising a rotating shaft rotating interlockingly with the object to be detected, an arc-shaped metal member fixedly arranged on a circular trajectory thereof with said rotating shaft serving as a center thereof, a sensor coil portion with a center axis along the circular trajectory, moving on the circular trajectory by interlocking the rotation of the rotating shaft, the sensor coil portion formed in an arc-shaped in order to freely adjust an occupation amount with respect to the magnetic circuit in response to the movement of the metal member into the center air-core of the sensor coil portion and a sensor circuit generating a signal corresponding to a rotation angle of the rotation shaft by detecting a magnetically change of the sensor coil portion generated in response to the movement of the metal member in the sensor coil portion under a condition that a modulated magnetic field with a high frequency is generated by driving and exciting the sensor coil portion.
A tenth aspect of the present invention, the sensor coil portion includes two sensor coils arranged such that sensors are arranged symmetrically with respect to a line passing through the rotation shaft serving as a rotation center, the arm portions extending from the middle point of the metal member are inserted into each sensor coil, respectively, when the rotation shaft rotates from the rotation angle 0xc2x0, the relationship between an occupation amount with respect to the magnetic circuit in response to the movement of one arm portion into the corresponding sensor coil and an occupation amount with respect to the magnetic circuit in response to the movement of the other arm portion into the corresponding sensor coil is maintained in the complementary change. The sensor circuit generates a signal corresponding he rotation angle of the rotation shaft on the basis of the magnetically change with respect to the both sensor coils.